JP2001274015A - Magnet roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnet roller which can prevent lowered productivity due to the formation of a groove of developing electrode, fogging of a developer due to low magnetic flux density on the downstream side of a developing part, and a drop of developing efficiency due to reduced quantity of dropping of magnetic flux density or blotting due to releasing of developer caused by reverse magnetic field, or the like, and which is inexpensive and optimal for reproducing a high-quality picture quality and coloring. SOLUTION: A plurality of magnet pieces as a developing magnetic pole are adhered to form a plurality of peaks of magnetic flux density having the same magnetic polarity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet roller incorporated in a developing roller, a cleaning roller, a transport roller and the like used in an electrophotographic copying machine, a printer, a facsimile and the like.

[0002]

2. Description of the Related Art A conventional magnet roller is disclosed in
-95243, JP-A-56-81868, JP-A-62-82
At 55149, a method of forming a plurality of magnetic flux density peaks having the same magnetic polarity by using one magnet piece for a developing magnetic pole and providing one or more grooves in the magnet piece, or forming a gap between two magnet pieces. A method has been reported in which a plurality of magnetic flux density peaks having the same magnetic polarity are formed by arranging and arranging in parallel (the orientation and magnetization directions are also parallel).

[0003]

Conventionally, a magnet piece which is magnetized in one direction and provided with a groove on the outer peripheral surface thereof is arranged in a developing magnetic pole portion, and a plurality of magnetic flux densities of the same magnetic polarity are provided in the developing magnetic pole portion. Had a peak. However, since it is necessary to form a groove in the magnet piece, the groove is formed by machining or the like after the magnet piece is formed, or the groove is formed by a mold at the same time as the molding. In these cases, cracks and chips are easily generated in the grooves, resulting in very poor productivity. Further, a plurality of magnetic flux density patterns having the same magnetic polarity, which are somewhat asymmetric, can be obtained by shifting the position of the groove from the center, but it is not sufficient. Further, the difference between the peak values of the magnetic flux densities of the same magnetic polarity cannot be increased (the conventional magnetic flux density difference is about 10 mT). In particular, in order to prevent the developer from fogging, only the downstream side of the developing section in the developer conveying direction is prevented. It is difficult to increase the magnetic flux density. (Although it is possible to increase the magnetic flux density peaks on both the upstream side and the downstream side by the conventional manufacturing method, in this case, the spike of the developer becomes hard, the developer is deteriorated, and the life of the developer is shortened.) The amount of magnetic flux density drop between the magnetic flux density peaks depends on the depth of the groove.However, it cannot be made too large due to the balance with workability. The drop amount of the magnetic flux density on the outer diameter φ24.5 of the sleeve φ22 was about 30 mT. The drop amount of the magnetic flux density is important in the developing property, and the larger the drop amount is, the more the developer is activated, the wider the width of the developer becomes, and the higher the developing efficiency is. The drop amount of the magnetic flux density here is obtained by the following equation. Depth = (average of magnetic flux density peaks of the same polarity)
-(Minimum value of magnetic flux density between the same magnetic polarities) Further, in a magnet roller in which two magnet pieces are arranged in parallel at an interval, see Japanese Patent Application Laid-Open No. 62-55 / 1987.
149, the directions of magnetization of the two magnet pieces are parallel and there is a gap between the two magnet pieces, so that the direction of the magnetic field in the gap is the direction from the magnet piece to the photoreceptor. The developer on the sleeve, which corresponds to the gap between the two magnet pieces, receives a force in the direction from the sleeve to the photosensitive member due to the opposite magnetic field in the gap. Therefore, the developer actively jumps out toward the photoreceptor, and the developer adheres to a portion that should not be developed, and as a result, the edge of the image blurs. The present invention prevents productivity deterioration due to the above-described groove formation,
Prevents developer fogging due to low magnetic flux density on the downstream side of the developing unit, and further causes reduction in developing efficiency due to small magnetic flux density drop and release of developer due to reverse magnetic field. It is an object of the present invention to provide a magnet roller that can prevent image bleeding and the like, can obtain high quality image at low cost, and is suitable for colorization.

[0004]

According to the present invention, as described in claim 1, a plurality of magnet pieces having the same magnetic polarity are attached to a developing magnetic pole without providing a gap between a plurality of magnet pieces having the same magnetic polarity. By forming the density peak, the generation of a reverse magnetic field between the same magnetic polarities can be prevented, the developer acting on the sleeve does not generate a force acting in the direction of the photoconductor, and the blur of the image can be prevented. By changing the amount of magnetization of the magnet piece, the magnetic flux density on the downstream side of the developing unit can be increased, and a high-quality image free of developer fog can be obtained. According to a second aspect of the present invention, a notch is not formed on the outer peripheral surface of the magnet piece of the developing magnetic pole portion, but a drop in magnetic flux density is formed between the magnetic poles. The magnetic flux density peak positions of two magnet pieces of the same magnetic polarity are set so as to be away from each other, and the sum of the angles of the orientation and magnetization directions of the two magnet pieces is 20 to 140 degrees, preferably 20 to 140 degrees. 80 degrees. With such a setting, it is possible to form a portion (a valley) where the magnetic flux density falls between the magnetic flux density peaks having the same magnetic polarity without forming a notch (a groove or the like) on the outer peripheral surface of the magnet piece. Therefore, the magnetic flux density can be reduced by using a magnet piece having a simple shape without machining a notch (a groove or the like) on the magnet piece, so that productivity is improved, and low cost and high quality are achieved. Image can be obtained.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Resin binder such as nylon (5% by weight to 50%
Weight%) and a magnetic powder (50% to 95% by weight) using a rare-earth exchange spring magnetic powder for N2 pole,
Except for the N2 pole, ferrite magnetic powder such as strontium is mixed and dispersed, melt-kneaded and formed into pellets, the pellets are melted, and a molten resin magnet material is injected and injected from an injection port. The magnet piece is formed by the above forming method. The magnet roller magnetization is 637 K · A / m by embedding permanent magnets in electromagnets or molds.
It is oriented and magnetized at the same time as molding with a magnetizing magnetic field of about 2387 K · A / m, or magnetized after molding. As shown in FIG. 1 (magnet roller cross-sectional view), each magnet piece molded by the above method is bonded to a shaft to form a magnet roller. In FIG. 1, the N1 pole and the N2 pole correspond to the developing magnetic pole, and the N2 pole is on the downstream side of the developing unit. The sectional shape of these magnet pieces is fan-shaped, and the magnetization orientation direction is θ1 = 0.
°, θ2 = 0 ° and are parallel. By doing so, it is possible to increase only the magnetic flux density peak value of the magnetic pole (N2 pole) on the downstream side in the developer conveyance direction at the same magnetic polarity of the developing unit. In the above-described manufacturing method, the magnetic powder for the N2 pole uses ferrite magnetic powder such as strontium as in the other poles as in the other poles, and the orientation magnetization directions θ3 = 20 ° and θ4 = of the N1 pole and the N2 pole as shown in FIG. 20 °, and the sum of the angles in the magnetization orientation direction was 40 °. With the above-described arrangement, it is possible to control the orientation and magnetization directions of the N1 pole and N2 pole magnet pieces without forming notches (grooves) on the outer peripheral surface of the magnet piece as in the related art.
A magnetic flux density pattern (two magnetic flux density peaks and a drop between the peaks) of the developing magnetic pole as shown in FIG. Also in FIG. 3, the N1 pole and the N2 pole correspond to the developing magnetic poles, and the magnet piece of the N1 pole has a fan-shaped cross section, but the N2 pole has a notch on the outer peripheral surface. By attaching the notched shape to the outer peripheral surface of the magnet piece in this way, it becomes easy to make the magnetic flux density pattern shape irregular as shown in FIG. Therefore, by appropriately selecting the shape of the magnet piece or the direction of the oriented magnetization, it is possible to meet various magnetic flux density pattern requirements. Further, as shown in FIG.
Notches are provided on the outer peripheral surfaces of the magnet pieces of the N1 pole and the N2 pole, and when these magnet pieces are bonded together, a recess is formed on the outer peripheral surface of the magnet due to each of the notches. The orientation and magnetization direction of each magnet piece is θ3 = 20 °, as in the magnet piece of FIG.
θ4 = 20 °, and the sum of the angles of the orientation magnetization direction was 40 °. In this way, by combining the control of the orientation and magnetization direction of each magnet piece and the shape of the magnet piece, the drop amount between the two magnetic flux density peaks of the developing magnetic pole can be further increased. When a high magnetic flux density is required on the downstream side of the developing section as shown in FIG. 1 or when a high magnetic flux density is required on the developing magnetic pole portion or all poles,
The magnetic powder used for the magnet piece may be a mixture of a ferrite magnetic powder and a rare earth magnetic powder (hybrid powder) or a rare earth magnetic powder alone. Examples of the rare earth magnetic powder include R (rare earth) -Fe-N alloy, R-Fe-B alloy, R-Co
Alloys and R-Fe-Co alloys. Among them, an exchange spring magnetic powder that includes a soft magnetic phase and a hard magnetic phase and has a structure in which the magnetizations of both phases exchange and interact may be used. The exchange spring magnetic powder has a low coercive force due to the soft magnetic phase and a high residual magnetic flux density due to the exchange interaction, so a high magnetic force can be obtained, and it is more resistant to oxidation than conventional rare earth magnetic powder. Rust can be prevented without surface coating such as plating, and a large amount of a soft magnetic phase is contained.
(C or higher) The operating limit temperature is high (about 200 ° C. or higher) and the temperature dependence of the remanent magnetization is reduced. R (rare earth element)
Are preferably Sm, Nd, Pr, D
One or a combination of two or more of y, Tb and the like can be used. In addition, Co, Ni, Cu, Zn, G
a, Ge, Al, Si, Sc, Ti, V, Cr, Mn,
Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, C
d, In, Sn, Sb, Hf, Ta, W, Re, Os,
One or more elements such as Ir, Pt, Au, Hg, Tl, Pb, and Bi can be added. As exchange spring magnetic powder, R-Fe-B as hard magnetic phase
Compound using Fe phase or Fe-B compound phase as soft magnetic phase, or R-Fe as hard magnetic phase
It is preferable to use an -N-based compound phase and an Fe phase as the soft magnetic phase. More specifically, an Nd—Fe—B alloy (soft magnetic phase: Fe—B alloy, αFe), Sm—Fe—N
Alloy (soft magnetic phase: αFe), Nd-Fe-Co-Cu
-Nb-B alloy (soft magnetic phase: Fe-B alloy, αFe
Exchange spring magnetic powders such as Nd-Fe-Co alloys (soft magnetic phase: αFe etc.) are suitable.
From the viewpoint of lowering the coercive force (iHc) and increasing the residual magnetic flux density (Br), Nd ₄ Fe ₈₀ B ₂₀ alloy (soft magnetic phase: Fe ₃ B, αFe) or Sm ₂ Fe ₁₇ N ₃ alloy (soft magnetic Phase: αFe) exchange spring magnetic powder is preferred. Further, as the ferrite magnetic powder, MO.Fe ₂ O
₃ Anisotropic or isotropic ferrite magnetic powder having a chemical formula represented by (n is a natural number) is used.
One type or two or more types such as Sr, Ba or lead are appropriately selected and used. The mixing ratio of the hybrid magnetic powder or the rare earth magnetic powder to the resin binder is as follows: magnetic powder: resin binder = 50% by weight to 95% by weight: 5% by weight to 50%.
% By weight, if necessary, a silane-based or titanate-based coupling agent as a surface treatment agent, an amide-based lubricant as a lubricant for improving the fluidity of a molten magnet material, a stabilizer for preventing thermal decomposition of a resin binder, Alternatively, a magnet roller or a piece is manufactured by injection molding or the like after mixing, dispersing, melting and kneading a magnet material to which a flame retardant or the like has been added, and molding into a pellet shape. 50% by weight of magnetic powder
If the amount is less than 70%, the magnetic properties of the magnet roller are deteriorated due to insufficient magnetic powder, and a desired high magnetic force cannot be obtained. If the content exceeds 95% by weight, the binder is insufficient and the moldability of the magnet roller and the piece is impaired. . Examples of the resin binder used for these include ethylene-ethyl acrylate resin, polyamide resin, polyethylene resin, polystyrene resin, PET, PBT, PP
There are S, EVA, EVOH, PVC and the like, and one or more of these can be used in combination.
In particular, when the main body is made of a resin binder made of nylon or the like, a thermoplastic resin such as PVC, an epoxy resin, a phenol resin, a thermosetting resin such as an unsaturated polyester resin, and a resin binder system having flexibility are used. Then, it is more preferable. The mixing ratio of the hybrid magnetic powder is as follows: rare earth magnetic powder: ferrite magnetic powder = 1: 9 to 9: 1.
It is preferable to adjust the range. The mixing ratio is 1: 9
If it is less than 10%, the content of the rare-earth magnetic powder is small, so that only a magnetic force equivalent to that of a conventional ferrite resin magnet can be obtained. If the mixing ratio exceeds 9: 1, a high magnetic force equivalent to that of a rare-earth resin magnet can be obtained. Since the mixing ratio of the magnetic powder becomes high, it is not desirable from the viewpoint of reducing the cost. here,
The technical terms “coercive force”, “residual magnetic flux density”, and “exchange spring magnetism” will be described. “Coercivity (iHc)”: The coercivity here is the intrinsic coercivity (i
Hc), which is an external magnetic field when only half of the remanent magnetization is maintained against the demagnetizing field due to the remanent magnetization. “Residual magnetic flux density (Br)”: Magnetizing force, that is, the magnetic flux density when the magnetic field is removed from the state of the saturated magnetic flux density. "Exchange spring magnetism": A large amount of soft magnetic phase exists in the magnet, and the magnetizations of the crystal grains having soft magnetic properties and the crystal grains having hard magnetic properties are connected to each other by exchange interaction, and the magnetization of the soft magnetic crystal grains is changed. The magnetization of the hard magnetic crystal grains hinders the reversal, and exhibits characteristics as if there were no soft magnetic phase. As described above, since the exchange spring magnet contains a large amount of the soft magnetic phase having a larger residual magnetic flux density and a smaller coercive force than the hard magnetic phase (usually a rare earth magnet alone), the coercive force is small and the residual magnetic flux is high. A magnet with a high density is obtained.

[0006]

According to the first aspect of the present invention, a plurality of magnet pieces having the same magnetic polarity are bonded together as a developing magnetic pole without providing a gap, so that a magnetic field in the opposite direction between the magnetic poles is not generated, and Unnecessary release is eliminated, image bleeding can be prevented, and by changing the amount of magnetization of each magnet piece, an asymmetrical magnetic flux density pattern can be formed, and especially the magnetic flux density on the downstream side of the developing unit is increased. By doing so, the developer fogging phenomenon can be prevented, a high quality image can be obtained at low cost, and a magnet roller suitable for colorization can be provided. According to claim 2, notches are not formed on the outer peripheral surface of the magnet piece of the developing magnetic pole portion, and the orientation and magnetization directions of the magnetic particles of each magnet piece are set so that the magnetic flux density peak positions are away from each other. As a result, the magnet piece can be easily formed without sacrificing productivity, a drop amount (valley) of the magnetic flux density between the same magnetic polarities can be obtained, and the developer in the developing magnetic pole portion is activated and It is possible to provide a magnet roller in which the width of the ears of the developer is widened, the developing efficiency is improved, high quality image is obtained, and the color roller is suitable.

[0007]

EXAMPLE 1 Nylon 12 was used as a resin binder in an amount of 10% by weight, and strontium ferrite (Sr
O.6Fe ₂ O ₃ ) and 90% by weight of a rare earth-based exchange spring magnetic powder (Nd ₄ Fe ₈₀ B ₂₀ ) for the N2 electrode, these are mixed, melt-kneaded and formed into pellets. The pellets were brought into a molten state, and a molten resin magnet material was injected and injected from an injection port to form each magnet piece shown in FIG. At the same time as molding, the magnetic field is 637 K · A / m to 238.
Orientation magnetization was performed in one direction at 7 K · A / m. The formed magnet piece was bonded to the outer peripheral surface of the shaft as shown in FIG. 1 to form a magnet roller. N1 pole, N
The fan opening angle of the two-pole magnet piece is θ1 = 30
°, θ2 = 30 °, and the orientation magnetization direction is θ3 = 0 °, θ
4 = 0 °. (The outer diameter of the magnet is φ22, the length in the magnet axis direction is 300 mm, and the axis is SUM22. The probe (sensor) is placed 12.25 mm away from the center of the obtained magnet roller, and the magnet roller is rotated. The magnetic flux density in the circumferential direction of the magnet roller was measured with a Gauss meter. As shown in FIG. 1, the angle from the angle reference (0 °) to the magnetic flux density peak position of the N1 pole (point A) is θ5, and the angle from the angle reference to the magnetic flux density peak position of the N2 pole (point C) is θ6. The angle from the angle reference to the magnetic flux density valley position (point B) between N1 and N2 is defined as θ7. The angle is defined as − in the clockwise direction and + in the counterclockwise direction from the angle reference. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Example 2 Nylon 12 was 10% by weight as a resin binder, and strontium ferrite (SrO.6Fe ₂ O ₃ ) was 9 as a magnetic powder.
The mixture was melt-kneaded and formed into pellets. The pellets were brought into a molten state, and a molten resin magnet material was injected and injected from an injection port to form each magnet piece shown in FIG. At the same time as molding, the magnetic field 637K
A / m to 2387 K. The orientation was magnetized in one direction at A / m. The formed magnet piece was bonded to the outer peripheral surface of the shaft as shown in FIG. 2 to form a magnet roller. The fan opening angles of the N1 pole and N2 pole magnet pieces are θ1 = 30 ° and θ2 = 30 °, and the orientation magnetization direction is
θ3 = + 20 ° and θ4 = −20 °. (The outer diameter of the magnet is φ22, the length in the magnet axis direction is 300 mm, and the axis is SUM22 with the diameter of φ8.) The measuring method of the magnetic flux density in the circumferential direction of the magnet roller was the same as in Example 1. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Example 3 The procedure was the same as Example 2 except that the orientation magnetization directions of the N1 pole and N2 pole magnet pieces were set to θ3 = + 10 ° and θ4 = -10 °. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Example 4 The procedure was the same as in Example 2 except that the orientation magnetization directions of the N1 pole and N2 pole magnet pieces were set to θ3 = + 40 ° and θ4 = −40 °. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Example 5 The procedure was the same as in Example 2 except that the orientation and magnetization directions of the N1 and N2 pole magnet pieces were set to θ3 = + 70 ° and θ4 = −70 °. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Example 6 As shown in FIG. 3, all operations were the same as in Example 2 except that a notch was formed in the outer peripheral surface of the N2 pole magnet piece. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Example 7 As shown in FIG. 4, all the operations were the same as in Example 2 except that the outer peripheral surfaces of the N1 pole and the N2 pole were notched. Table 1
7 shows the magnetic flux density and magnetic pole position of the developing magnetic pole portion. Comparative Example 1 A conventional magnet roller is shown. As shown in FIG.
One pole and N2 pole are made into one magnet piece, and a notch (groove) is made near the center of the outer peripheral surface of this magnet piece.
All were the same as in Example 2 except that. In Table 1,
The magnetic flux density and magnetic pole position of the developing magnetic pole portion are shown. Comparative Example 2 The procedure was the same as in Example 2 except that the orientation magnetization directions of the N1 pole and N2 pole magnet pieces were θ3 = + 5 ° and θ4 = −5 °. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Comparative Example 3 The procedure was the same as that of Example 2 except that the orientation magnetization directions of the N1 pole and N2 pole magnet pieces were set to θ3 = + 80 ° and θ4 = −80 °. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. Comparative Example 4 Comparative Example 1 was carried out in the same manner as Comparative Example 1 except that the notch depth (groove depth) was increased within the moldable range. Table 1 shows the magnetic flux density and magnetic pole position of the developing magnetic pole. As is clear from the results shown in Table 1, as shown in Example 1, since the developing magnetic pole portion is composed of two magnet pieces, the magnetic characteristics of each piece can be changed. By using a rare earth-based exchange spring resin magnet having high magnetic properties for the N2 pole, a high magnetic flux density value can be obtained on the N2 pole side, and the difference between the magnetic flux peak peak values of the same magnetic polarity becomes 15 mT or more. A magnetic flux density difference larger than about 10 mT of the magnetic flux density peak value can be obtained. In the second embodiment, the developing magnetic pole is composed of two magnet pieces and no notch is provided on the outer peripheral surface of the magnet piece. Compared to Comparative Example 1 of the manufacturing method, it can be seen that a magnetic flux density pattern of almost the same level was obtained. Therefore, even with a relatively simple shape in which no cutout is provided on the outer peripheral surface of the magnet piece, a conventional level of magnetic flux density pattern (magnetic flux density peak value and magnetic flux density drop amount) can be obtained. Further, since the magnetic flux density drop between the same magnetic polarities is required to be 5 mT or more in practical use, the magnetic flux density falls within the range shown in Examples 2 to 5, that is, the sum of the magnetization directions of the magnet pieces is 20 ° or more and 140 ° or less. We can see that we can do it. Considering the decrease in the peak value of the magnetic flux density of the same magnetic polarity, the sum of the magnetization directions is 20 °.
~ 80 ° is more preferred. When the sum of the magnetization directions is less than 10 °, as shown in Comparative Example 2, the drop amount is less than 5 mT, so that there is practically no effect of two magnetized polarities, and the sum of the magnetization directions is 140 °. In the case where the width exceeds the predetermined value, the magnetic polarity of the recessed portion becomes the reverse polarity, and as a result, the width of the spike of the developer becomes small, so that the development efficiency is reduced and high image quality cannot be obtained. As shown in the sixth embodiment, by providing a cutout on the outer peripheral surface of the N2 pole magnet piece, it is also possible to obtain an asymmetric magnetic flux density pattern at an angle reference (0 °). The drop amount of the magnetic flux density between the same magnetic polarities in Example 7 is 37 mT, whereas the drop amount in Comparative Example 4 is 31 mT. It can be seen that the depth of Example 7 is larger than that of Comparative Example 4 in which the groove depth is maximized.
Also, in this case, it can be seen that the magnetic flux density at point A and point C is larger in Example 7 than in Example 7. Therefore, by providing a cutout on the outer peripheral surface of the magnet piece as in the seventh embodiment, a high magnetic flux density having the same magnetic polarity can be obtained, and a large drop in the magnetic flux density between the same magnetic polarities can be obtained.
It is possible to obtain a magnet roller that is optimal for high image quality.

[Table 1]

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnet roller of the present invention and a magnetic flux density pattern in a circumferential direction.

FIG. 2 is a sectional view of a magnet roller of the present invention and a magnetic flux density pattern in a circumferential direction.

FIG. 3 is a sectional view of a magnet roller of the present invention and a magnetic flux density pattern in a circumferential direction.

FIG. 4 is a sectional view of a magnet roller of the present invention and a magnetic flux density pattern in a circumferential direction.

FIG. 5 is a sectional view of a conventional magnet roller and a magnetic flux density pattern in a circumferential direction.

FIG. 6 is a sectional view of a conventional magnet roller and a magnetic flux density pattern in a circumferential direction.

[Explanation of symbols]

 1. Magnet piece 2. Sleeve 3. Axis 4. 4. Circumferential magnetic flux density pattern 5. Angle position reference line (0 °) Notch

Claims (2)

[Claims] 1. A magnet roller wherein a plurality of magnet pieces are bonded as developing magnetic poles to form a plurality of magnetic flux density peaks having the same magnetic polarity. 2. The magnet roller according to claim 1, wherein a notch is not formed on the outer peripheral surface of the magnet piece at the developing magnetic pole portion, and the orientation and magnetization directions of the magnetic particles of each magnet piece are not parallel.